Heart of Midlothian centre-half John Souttar has been called into the Scotland squad following the withdrawal of Norwich City's Grant Hanley.
Newcastle United winger Ryan Fraser has also dropped out of the squad to face Moldova and Denmark in World Cup qualifiers.
Souttar earned the last of his three caps in October 2018, when he was sent off in a 2-1 defeat by Israel.
The 25-year-old's progress has since been blighted by serious injury.
However, he has made 15 appearances this season for a Hearts side sitting third in the Scottish Premiership.
Norwich revealed Hanley's groin injury ahead of the centre-back missing his side's 2-1 win over Brentford on Saturday, while Fraser was an unused substitute as Newcastle drew 1-1 with Brighton & Hove Albion.
Scotland can secure second spot behind the Danes to earn a play-off place to qualify for the 2022 finals in Qatar if they beat Moldova in Chisinau on Friday.
Steve Clarke's side would still finish runners-up in Group F with a draw as long as Austria hold Israel to a draw on the same evening.